1. Field of the Invention
The invention relates to foundry and more particularly to equipment for manufacturing foundry cores in a heated tooling.
The invention can be employed at automotive, sanitary engineering, electrical engineering, machine building and other industrial production works inherent to which is a large-lot and mass character of production.
2. Description of the Prior Art
In recent years, methods for manufacturing foundry cores directly in core boxes have found extensive application in world practice, these being the so-called "hot-box" and "cold-box" processes.
The "hot-box" process provides for the manufacture of cores by blowing a core sand composed of sand, a binder and a catalyst into a heated core box. The core sand hardens under the action of heat and of the catalyst through a rapid polymerization of the binder. Foundry machine building works manufacture a range of multi-station apparatus operating on the "hot-box" principle. The apparatus includes a core-blowing machine, devices for disassembling core boxes and delivering finished cores, a device for heating the core boxes and a transportation means for moving the core boxes from one station to another.
The apparatus operates as follows.
In the first station, a hot box is pressed against a sand-blowing plate and filled with sand. The second station is intended for inspecting and changing the core boxes. Next, the sand hardens in several stations, as the core boxes are heated by either passing them through a heating chamber or energizing heaters built into them. In the last station, the core boxes are opened and, after a finished core is removed, blown with compressed air.
The "cold-box" process provides for the manufacture of cores by blowing a cold core box with sand and a subsequent hardening thereof either through blowing by a gaseous catalyst (Ashland cold-box process) or the use of a highly reactive binder with a greater amount of catalyst (Fascold or Gisag cold-box process).
Equipment for manufacturing foundry cores on the "cold-box" principle has become widely known.
Overall, the equipment operating on the "hot-box" and "cold-box" principles, while enhancing efficiency, increasing strength of sand and improving working conditions, fails to provide an effective ventilation of cores, in particular, such as cores for heating boilers and radiators which are cast with metal on all sides and, except for two small core prints, are out of contact with a mould. As sand hardens uniformly throughout the cross section, vents in cores are obtained and communicated with the atmosphere by manufacturing cores of two halves which are glued together. These additional process operations substantially complicate the manufacture of cores, raise labour requirements, prejudice geometric and dimensional accuracies of cores, hinder a complex automation of core manufacture.
There are known a method and an apparatus for carrying the method into effect which are free of the above shortcoming (see FRG Pat. No. 2,239,057, cl. B 22 C 9/10).
The method consists in that a fluid sand is pressed into a heated core box, the core box is sealed tight, then, after a specified holding necessary to harden the sand, a finished core is removed.
The method enables any cores to be fabricated in a single piece, as a natural canal or porosity is formed in the middle of the core in the course of hardening through which gases can be effectively vented. The apparatus is composed of capacities and batchers of starting sand components, a mixer with a gate shutting off a discharge port, a pressing cylinder with a ram, a batching chamber, a sliding damper with an expansible nozzle, a lifting table, and operates in the manner below.
Starting components of the sand are fed into the mixer, stirred therein, moving in the process toward the discharge port, where a finished fluid sand is formed and transferred into the batching chamber having the damper in its bottom part. Once the batching chamber is filled with sand, the gate closes the discharge port of the mixer, the damper slides to align the nozzle with the batching chamber, while the table lifts and forces a heated core box against the nozzle. The ram is acted upon by a pressing cylinder to pack sand into the core box. Once this is completed, the core box is sealed to prevent sand from being ejected through the inlet opening. After a certain time necessary for the foam to abate and the sand to lose mobility, the core box can be transferred to a next station. The damper closes again the bottom of the batching chamber, the ram returns to initial position, and the gate opens the discharge port of the mixer. The cycle is then repeated.
The pressure in the core box may rise under a certain set of conditions and attain a value sufficient for overcoming the weight of the top half of the core box. Therefore, if a core box, after it has been packed and sealed, is held at the pressing position for a certain period of time, the top half thereof will be forced up, and some sand will be spilled out along the parting plane, this unavoidable resulting in a defective core.
Sand hardening requires much more time as compared to the "hot-box" and the "cold-box" processes, since hardening takes place mainly through vaporization of moisture from the fluid sand.
The prolonged holding of the core after sand is pressed and the greater sand hardening time lead to a substantially longer core manufacturing cycle and thus appreciably lower both the efficiency of the machine as compared to equipment operating on the "hot-box" and the "cold-box" principles and, therefore, the advantages the machine may offer in large-lot and mass production runs.
A material disadvantage of the known machine is that it lacks in devices permanently fastening together the halves of a core box from the moment it is packed to the moment it is opened. A fairly long holding of a core box compressed between the table and the pressing mechanism, once the sand has been packed, necessary to allow the sand pressure in the core box to fall off sufficiently and so prevent the top of the core box from being lifted once the core box is set free, brings down the efficiency fo the multi-station machine, and in the final analysis, provides no absolute guarantee that the top half of the core box will not be dislodged vertically by the residual pressure. A result of these movements may be a distortion of geometric dimensions of cores and a poorer quality thereof.